(1) Field of the Invention
The present invention relates to an apparatus and method for treatment of a surface using a plasma generated by a microwave or UHF power source wherein the plasma is focussed below an orifice leading from a chamber in a region containing a substrate. The apparatus and method generates a high power density plasma adjacent to a surface. In particular, the present invention relates to a method for the rapid deposition of a material, such as diamond, by plasma assisted chemical vapor deposition on a portion of the surface of an object with a complex geometry, such as a drill or a seal ring. The present invention preferably uses internal applicator tuning, wherein an excitation probe and sliding short are used for internal tuning to minimize the reflected microwave or UHF power and to focus the plasma in the region, when the other experimental parameters such as a substrate, a substrate holder, a substrate position, input power, gas flow, pressure, and the like are changed. This allows easy optimization of the treatment.
(2) Prior Art
Improved methods for depositing a film of a material on a substrate has always been an important goal of scientific and industrial research. The need to coat materials with thin films leads to an interest in the design and construction of an efficient apparatus.
There is no reliable commercial method which is economically feasible for diamond film deposition on complex geometries, such as drill bits and seal rings. This is primarily due to the difficulty of creating a uniform plasma around these complex geometries. This is especially true if the objects to be coated are electrically conductive. Conductive surfaces of these objects interfere with the formation of the plasma.
Diamond, having unique mechanical, optical and electrical properties, is one of the most valuable scientific and technological materials. Ever since Tennant discovered that diamond is made of carbon in 1797, synthesis of diamond has long been a goal of research effort of numerous individuals. In 1955, Bundy and co-workers succeeded in the reproducible synthesis of diamond (Bundy, F. P., et al., "Man-made diamond," Nature 176 51 (1955)) with a molten transition metal solvent-catalyst at pressures where diamond is the thermodynamically stable phase of carbon.
Diamond growth at low pressures where graphite is the stable carbon phase can be traced back to W. G. Eversole (Eversole, W. G., U.S. Pat. Nos. 3,030,187 and 3,030,188); Angus et al (Angus, J. C., et al., J. Appl. Phys. 39 2915 (1968); and Deryaguin et al (Deryaguin, B. V., et al., J. Cryst. Growth 2 380 (1968)), but the low growth rate (less than 0.1 micrometer per hour) was not practical and prevented commercial interest at that time. The breakthrough in the synthesis of diamond at low pressures came in the late 1970's and early 1980's, when a group of Soviet researchers (Spitsyn, B. V., et al., J. Cryst. Growth 52 219 (1981)) and Japanese researchers (Matsumoto, S., et al., Jpn. J. Appl. Phys. 21 part 2, 183 (1982)) published a series of research papers on diamond film growth at higher growth rate (several micrometers per hour) from hydrocarbon-hydrogen gas mixtures. Since then, numerous techniques have been developed for diamond film growth at low pressures. These techniques can be divided into five major categories: (1) thermally activated or hot filament activated chemical vapor deposition (CVD) (Matsumoto, S., et al., J. Appl. Phys. 21 part 2, L183 (1982); Matsumoto, S., et al., J. Mater. Sci. 17 3106 (1982)); (2) high frequency plasma enhanced CVD (Kamo, M., et al., J. Cryst. Growth 62 642 (1983); Matsumoto, S., et al., J. Mater. Sci., 18 1785 (1983); Matsumoto, S., J. Mater. Sci. Lett., 4 600 (1985); Matsumoto, S., et al., Appl. Phys. Lett., 51 737 (1987)); (3) direct current discharge enhanced CVD (Suzuki, K., et al., Appl. Phys. Lett., 50 728 (1987)); (4) combustion flame (Hirose, Y., et al., New Diamond 4 34 (1988)); and (5) other and hybrid techniques. All of these techniques are based on the generation of atomic hydrogen and carbon containing species near the thin film growing surface.
A very common method of synthesis is microwave plasma assisted CVD. This method has shown excellent potential for growing high quality diamond films and variations of this technique are now in common use in many laboratories and industries. Since there are no metallic electrodes present in the microwave plasma, the problem of metallic contamination in the process of diamond deposition does not exist. Compared to the erosion of electrodes in direct current reactors, microwave plasma diamond film deposition is a cleaner process. It is also easier to control and optimize the deposition process which makes microwave plasma reactors the most promising technique for stably growing pure and high quality diamond films (Deshpandey, C. V., et al., J. Vac. Sci. Technol. A7, 2294 (1989); Zhu, W., et al., Proc. IEEE 79, No. 5, 621 (1991)).
High rate diamond film deposition has been achieved by several different apparatus. A DC discharge jet diamond film reactor apparatus is shown in S. Matsumoto, et al., Jpn. J. Appl. Phys. 29 2082 (1990). In this reactor, the input gas which is a mixture of Ar, H.sub.2 and CH.sub.4 is dissociated by a DC voltage V.sub.d across the electrodes. A high temperature discharge jet is created and sustained by a DC power supply. The substrate is mounted downstream of the jet stream on a water-cooled substrate stage. Diamond film is formed on the substrate when the dissociated gas species react on its surface. A bias voltage V.sub.b is used to enhance the film growth rate. The typical experimental conditions are: Ar flow rate=30 l/min, H.sub.2 flow rate=10 l/min, CH.sub.4 flow rate=1 l/min, pressure=140 Torr, discharge voltage=70-76 V, discharge current=133-150 A, bias voltage=0-500 V, bias current=0.5 A, substrate=Mo plate of 20 mm in diameter, distance between the substrate and nozzle=57-102 mm, substrate temperature=700.degree.-1100.degree. C., deposition time=10 min, substrate pretreatment=scratched with 5-10 .mu.m particle size diamond paste for about 5 min.
A microwave jet reactor is also shown in Y. Mitsuda, et al., Rev. Sci. Instrum. 60 249 (1989) and K. Takeuchi et al., J. Appl. Phys. 71 2636 (1992). The input gas, which is a mixture of hydrocarbon, hydrogen and oxygen, is dissociated near the jet nozzle by the microwave energy. Microwave energy is transmitted from the power source to the jet nozzle through TE.sub.01 mode in the rectangular waveguide, a transition unit and TEM mode in the coaxial waveguide. The plasma jet is generated from the end of the center plasma flow stabilizer and blows through a constriction or nozzle and into the deposition chamber where the substrate is placed on a water-cooled substrate holder. Diamond film is formed on the substrate when the dissociated gas species react on its surface. Note that the microwave discharge is created upstream from the nozzle, allowing gas by-passing of the discharge. Diamond films have been deposited under the following experimental conditions: substrate=Si, Ar flow rate=10 l/min, H.sub.2 flow rate=20 l/min, CH.sub.4 flow rate=0.6 l/min, O.sub.2 flow rate=0.15 l/min, total pressure=760 Torr, substrate temperature=887.degree.-927.degree. C., microwave power=3.8-4.2 kW. The diameters of the center and outer conductor in the coaxial waveguide are 20 and 57.2 mm, respectively. The conductors taper off and play the roles of plasma flow stabilizers for plasma generation. These stabilizers are made of water-cooled copper in order to prevent thermal evaporation. The edge of the outer electrode (plasma jet nozzle) is 22 mm in diameter, which must be designed properly depending upon the plasma gas composition.
To successfully commercialize diamond synthesis at low pressures, diamond growth at high rates is desirable. The reactors described previously can deposit diamond film and growth rates in the order of 100 .mu.m/hour. But in these jet reactors, the reactive gases flow through a discharge which is located upstream from a nozzle. The hot gases are then forced through the nozzle and projected onto a substrate. In addition to gas flow by-passing of the discharge, there is significant amount of volume and surface recombinations of dissociated reactive species when they are forced through the nozzle. The gas flow and power efficiencies of the reactors are significantly reduced. Also, when hot gases are forced through a nozzle, the problems of nozzle erosion and/or deposition and/or melting exist.
The apparatus described in U.S. Pat. No. 5,311,103 issued to the present inventors is used to create a uniform coating on surfaces. The apparatus was difficult to use in reproducibly coating surfaces with complex geometries such as ring seals and drills. The problem was especially evident if the surface to be coated was electrically conductive. Conductive surfaces of these objects to be coated interfere with electromagnetic fields in the cavity and make it very difficult to form a plasma around the surface.
There is further a need for an apparatus and method for uniform etching of a surface with a plasma. Such etching is used for silicone chips and the like.
There is a need for a microwave apparatus for plasma deposition of diamond and diamond film coating on surfaces of objects with complex geometries, such as drill bits and seal rings. There is also a need for an apparatus and method for uniform plasma etching.